A large amount of formation water, brine, is co-produced when oil and gas are pumped to the surface from formations deep in the Earth. It is not unusual for 10 barrels of water to be produced for each barrel of oil. Generally, producing formations are very deep (on the order of 12,000 ft). At these depths it is very hot and the formations are under high pressure. The waters are saturated with many ingredients that are dissolved from the substrata. As they are brought to the surface brines from different reservoirs may become mixed, and temperatures and pressures drop. These changes promote precipitation and condensation reactions. The solutes along with suspended particulates form deposits (scale) on and in the production equipment, and sediment particles composed, at least in part, of precipitated inorganic materials, and rock fragments derived from the producing formation accumulate with oil in tanks and transfer tubing as sludge.
The inorganic compositions of the scales and sludges comprise barite (BaSO4), celestite (SrSO4), anhydrite (CaSO4), witherite (BaCO3), strontianite (SrCO3), calcite (CaCO3) and numerous other components among which may include metallic inclusions of Pb, Cu, Zn, and Ag (Saunders and Rowan, 1990). Radium co-precipitates with the other alkaline earth elements rendering the scales and sludges radioactive. Hydrocarbon production scales and sludges have been reported to contain 226Ra activities of anywhere from zero to several thousand Bq/g.
Naturally occurring radioactive material (NORM) is a broad classification that includes any radioactive, naturally-occurring material. Because these solid byproducts of hydrocarbon production contain radium, and the radium content has been enhanced through precipitation reactions as the result of the production of hydrocarbons, they could also be referred to as technologically enhanced NORM i.e. TENORM. It has been estimated that, when all oil and gas field NORM containing scales and sludges are included, between 3×105 and 1×106 tons are produced every year in the United States.
Scale formation can cause restriction or blockage of piping and may cause malfunction of equipment. Maintenance involves periodically removing the scale and sometimes replacing the tubing and other equipment. Sludge buildup in storage tanks reduces their capacities and hinders their operation. Thus, the sludge must also be periodically removed. Each year scale and sludge formation costs hydrocarbon producers millions of dollars in maintenance, treatment, and lost production time. While brines are often disposed of by pumping into injection wells, scales and sludges that contain NORM fall under strict and expensive governmental disposal regulations.
Radium co-precipitates with alkaline earth elements of scale and sludge, rendering these radioactive. The scales and sludges are highly insoluble. In the past, few disposal methods have been available, and many have been based on treating the scale and sludge as low level, solid radioactive waste. Solid radioactive waste disposal is expensive, and presents numerous liability issues for the producer.
At the present time there are few means of disposing of radioactive scale and sludge produced as by-products of oil and gas production. One is “land spreading”, where the material is spread on the surface of the ground, tilled into the top of the soil, and then covered with a layer of “clean” soil. After covering, if the level of radioactivity is below governmental action levels, the site may be considered uncontaminated.
Another method is to bury the radioactive scale and sludge in a lined pit, where the material is placed in a pit with a water-impermeable liner, covered with a water-impermeable liner, and then covered with soil.
Another method is to store the scale and sludge in drums at low-level radioactive material storage sites. Several producers of such scale and sludge are required to temporarily store the sludge and scale materials at the production sites over gravel beds, on impermeable liners, while awaiting shipment to storage facilities.
Other methods include dissolution of the sludge and scale with acid and chelation treatment, followed by re-injection into the producing formation. Also, other methods include grinding the solids to a fine particulate, followed by slurrying with water, and re-injection into the producing formation.
Additionally, the radioactive waste material has been used to fill spent well bores, followed by capping with concrete.
There are obvious disadvantages to each of the disposal options outlined above.
For example, disposal at low level radioactive waste storage facilities is expensive, and it generally involves shipping the material from the site where it was produced to a distant site with the attendant transportation risks.
Disposal by land spreading has exposure dangers. Most of the government regulations that allow land spreading also allow the land to be released for unrestricted usage afterward. Additionally, it is unlikely that the material will remain undisturbed for any extended time period after it is deposited. Erosion, burrowing animals, and construction are just some of the ways that the land may be disturbed subsequent to the land farming options.
Disposal by re-injection of slurried powder in water is probably the most permanent and liability free means of disposal, but it is also the most expensive and lowest capacity means of disposal. Enormous pumping pressures are necessary to re-inject slurried solids back into the original formation. In addition, the required pumping pressures consume large quantities of fuel to run the pumps making the process almost prohibitively expensive. A variation of the process involves “fracturing” the formation. This increases the porosity of the rock by creating cracks in the rock, which eases the re-injection process, but it comes with the risk of allowing the material to comingle with other geologic formations including potable ground waters. However, there are advantages to re-injection methods. For example, re-injection serves to keep the formation pressurized, which increases the productive life of the formation.
Since this naturally occurring radioactive material in oil field and gas field waste is becoming a major problem and an increasing burden for oil and gas production companies, the need exists for a simple, effective, and even portable method to effectively treat and deposit such wastes.
The present invention helps meet those needs.